What is an Oil Seal?

Oil seals, also referred to as shaft seals, are widely used to prevent the leakage of medium (such as oils and grease) along a rotating shaft. This leak prevention is primarily achieved by the sealing element which can be made from a wide range of materials that are chosen according to each application. They are commonly used in gearboxes, hydraulic cylinders, and related components.

Purpose of an Oil Seal

An oil seal is designed to perform three major functions: to prevent lubricants from leaking outside the seal even under high pressure, to act as a barrier to retain the lubricating oil, and to prevent dirt and other contaminants from entering the unit.

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Construction of an Oil Seal

Oil seals normally consist of three basic components: the sealing element, the metal case, and garter spring.

1. Sealing Element

The sealing element makes up the interior of the oil seal, and the materials commonly used are:

• a. Nitrile Rubber (NBR) – this is the most commonly used material. It has good heat resistance properties and has good resistance to salt solutions, oils, hydraulic oils, and gasoline. Operating temperatures are recommended from -40 to 248⁰ F (-40 to 120 deg.C). Nitrile also functions well in a dry environment, but only for intermittent periods. The disadvantage of this material is poor chemical resistance.
• b. Polyacrylate Rubber (PA) – also known as acrylic rubber, this material has better heat resistance than nitrile. PA is also recommended for a high surface speed environment. Operation temperatures are recommended from -4 to 302⁰ F (-20 to 150⁰ C). Polyacrylate rubber should not be used with water or in temperature below -4⁰ F (20⁰ C).
• c. Silicone Rubber (SI) – these compounds operate effectively in a broad temperature range of -58⁰ F to 356⁰ F (-50 to 180⁰ C). Silicone rubber is a leading choice for its resistance to both low temperatures and heat. The high lubricant absorbency of the material minimizes friction and wear. These oil seals are usually used as crankshaft seals. Silicone has poor resistance to hydrolysis and should not be used in oxidized or hypoid oils.
• d. Fluorocarbon Rubber (FKM) – is widely known under the Chemours (formerly Dupont™) trade name of Viton® and offers the best resistance to chemicals and superior performance to high temperatures.

2. Metal Case

The metal case is the exterior (or frame) of the oil seal, the principal function of which is to give rigidity and strength to the seal. The material of the case must be selected depending on the environment where the seals are to be used. Often the metal case is covered by the same rubber material used in the sealing element, which also helps seal the exterior of the oil seal in the housing bore. Common case material types are:

• a. Carbon Steel – the most common material used in oil seals.
• b. Stainless Steel – for applications that require resistance to water, chemicals, or corrosion. (Stainless steel metal cases are also recommended for many FDA applications.)

3. Garter Spring

The garter spring is located at the end of the primary sealing lip and used to apply pressure to the sealing lip against the shaft. Common garter spring material types are:

• a. Carbon Steel – which is used in conjunction with regular lubricants.
• b. Stainless Steel – which is used when resistance to water, seawater, and chemicals are involved.

Oil Seals From Global O-Ring and Seal

Global O-Ring and Seal carries a full line of oil seals in all industry standard sizes and has the ability to create custom oil seals. If you are a distributor or user of oil seals who may have need for our services, contact us today to speak with one of our team members, request a no-obligation quote, or place an order from our extensive inventory at GlobalOring.com.

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Want to learn more? Read “Oil Seals 101, Part 2”.

PRESIDENT/OWNER:
Bill has served in the sealing industry for more than 25 years, and founded Global O-Ring and Seal nearly 10 years ago.

Which is the Best Material for Your Oil Seal?

An oil seal is basically a simple device, which is used to stop dirt, dust, water, and other contaminants from entering the shaft equipment. It is also known by other names like elastomeric lip seal, lip seal, shaft seal, or rotary shaft seal. The seal, while doing its job, helps retain the lubrication of a rotary shaft equipment. These seals are mainly used to protect the bearings used in a rotating shaft.

Materials Used to Make Oil Seals:

Oil seals can be made from a vast range of materials depending upon the application. Some common materials used to manufacture oil seals include:

1. Silicone: The widest range of operating temperature range is provided by silicone compounds. They offer an amazing temperature range from -90°F to 340°F. Nonetheless, in dry running conditions, these compounds do not perform well. It is always advisable to avoid the usage of silicone compounds with oxidized oils and EP (Extreme Pressure) compounds.
2. Viton®: Viton® compounds are said to offer the widest operating temperature range varying from 40°F to 400°F. These are considered as the premium materials for the lip seals. In addition to this, these compounds are highly resistant to chemicals and abrasion. These qualities help Viton® deliver better good performance. Unlike silicone compounds, Viton® performs well in dry running applications.
3. Nitrile Buna-N: Most companies consider Nitrile Buna-N 70 durometer compound to be the perfect material for oil seals. The compound has several benefits, which makes it the first choice of material in a wide range of applications. Oils seals that are made from this material have a wide operating temperature range from -65°F to 250°F. In addition to this, this material is compatible to work with water, as well as common mineral oil and greases.

Above mentioned are some materials used for manufacturing oil seals. Each material has its own set of pros and cons. Therefore, selection of materials should be made on the basis of the application. There are quite a variety of materials to choose from. If you find it tricky to select the right material for oil seals, you can always ask an expert. SSP Manufacturing, Inc. is one such expert in manufacturing oil seals in the USA. Please contact us by Phone: +1-888-238-7325 or email rrom@sspseals.com with any questions.

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The sealing part, the metal case, and the spring are the standard three parts of an oil seal. The sealing component aims to prevent fluid leakage between the shaft and housing. The metal case will offer stiffness and strength as the seal is retained in the bore or recessed groove. The garter spring maintains radial force on the shaft and constant pressure, flattening the sealing edge to a specified width. In addition, the garter spring maintains the sealing lip's radial force around the shaft surface. The environment the oil seal will operate must be considered when choosing any material.

An appropriate unit load must be kept at the seal-shaft interface for these seals to work as intended. These seals can withstand 15 psi of pressure, and their performance is influenced by factors such as shaft diameter, speed, operating temperature, service circumstances, etc. Any rotating and moving parts combination must include oil or shaft seals. Oil seals are widespread in hydraulic cylinders, gearboxes, etc. The seals are also known as "dynamic oil seals" since they are used in places where motion is an issue.

• The function of the oil seals is to serve as a physical barrier that keeps the lubricant in the designated area.
• Second, they stop the lubricating oil from leaking outside despite high pressure.
• Third, it serves as a barrier to keep debris, contaminants, and other outside elements out of the system that contains the lubricating oil.

Constructional Aspects of an Oil Seal

• The inner skeleton of the oil seal, which gives it structural support, is an inner metal ring.
• Nitrile rubber and other materials, employed depending on the need, are used to make the outer skin.
• The spring on the oil seal's lip tends to support the lip while preventing leakage of the lubricant outside and the admission of foreign pollutants.

Types of Oil Seals

Double Lip Oil Seals

Along with the standard sealing lip, this also has an auxiliary lip. This type is advised for usage in polluted areas because the additional dust lip shields the main sealing lip from dust and other fine solid pollutants. Again, a sufficient lubricant should be used between the two sealing lips to achieve a long lifespan.

Advantages

• reduced likelihood of fretting corrosion
• good static sealing
• compensating for varied thermal expansions
• installation in split-housings
• modern lip design offers reduced radial forces
• effective protection against airside pollutants
• Higher bore surface roughness is permitted.

Duplex Oil Seals

Occasionally, two distinct fluids will mix after leaking from one chamber to another. This kind is advantageous in this case. This duplex-type oil seal with metal inserts is suggested for use on assemblies where it's important to avoid mixing different fluids.

Oil Seals Without Spring

This kind of oil seal may tolerate only very little speed and friction. It is advised in locations that must be sealed off from thick fluid or grease. For challenging applications, this is not advised.

Materials Used on Oil Seals

Nitrile synthetic rubber is used to make oil seals, and steel stiffener rings are used. Other rubbers like Viton™, silicon, neoprene, or poly acrylic can be utilized for particular uses. For example, brass or stainless steel stiffener rings may be used when sealing extremely corrosive fluids. For corrosion resistance, most springs are composed of spring steel that meets IS 4454:Gr.ll standards, stainless steel, or bronze.

Type A Oil Seals

The interference fit between the flexible sealing element, often strengthened by spring pressure, and a shaft leads to the sealing of lip-type seals in most cases. Fluid retention is determined based on the precise amount of lip contact pressure. Most lip seals experience increased lip contact pressure on the shaft due to higher fluid pressure in the sealed area.

Advantages

• reduced likelihood of fretting corrosion
• good static sealing
• compensating for varied thermal expansions
• Installation in split housings is permitted, allowing for a higher bore surface roughness, and a modern lip design offers minimal radial forces.

Metal-Cased Oil Seals

Metal-cased oil seals are used when affixed to a housing bore of the same material. Due to the materials' ability to operate with equal levels of contraction and expansion, leakage is prevented. Generally speaking, rubber seals cost more than metal-cased seals.

Rubber-Cased Oil Seals

Rubber-cased oil seals are the most widely used oil seal implementation when a metal-cased oil seal has a probability of failing (for example, because of thermal expansion). In contrast to oil seals with metal casings, rubber-cased oil seals cannot rust. Additionally, oil seals with rubber cases are much more effective in sealing a housing with little damage than oil seals with metal cases. Fast-expanding rubber can provide a tight fit and more stable sealability at high temperatures and pressures.

The one that is used frequently is Type R. This kind has a carbon steel insert and a rubber outside diameter. Rubber has a great sealing ability even if the housing is not entirely within tolerance. The sealing lip with spring produces obstruction on the shaft for effective sealing. The outside diameter and inner metal reinforcement casing enable press-fitting in the housing with adequate interference on the rubber to ensure static sealing.

The sealing part is made out of nitrile rubber. Thanks to this and a high-quality galvanized steel garter spring, this oil seal has the longest lifespan conceivable. To prevent leaks brought on by a hydrodynamic pumping action, the sealing lip contact area on the sleeve or shaft must be devoid of any indications of machine life.

Type B Oil Seals

Type “B” oil seals resemble an "A" style seal. But, on the other hand, this has a metal case outside. This type is preferred with rugged housing, hot environments, and demanding jobs.

Advantages

• Excellent fitting stability prevents the seal from popping out.
• Low radial forces are provided by modern lip design.
• outstanding radial rigidity, particularly for very large diameters
• suitable for usage in conjunction with an axial seal
• cost-effective for pricey elastomer materials

The outer layer of the skin often varies depending on how the oil seal is applied. Here are some materials used to make this oil seal's exterior skin.

• The material that is frequently utilized for oil sealing is nitrile rubber.
• Silicone is used in specialized applications with minimal stress.
• Polyacrylate fluoroelastomer is also referred to as Viton™ in popular culture. When temperatures exceed 120° Celsius, high temperature-resistant materials such as this are utilized.
• Polytetrafluoroethylene (PTFE)

Factors to Consider When Using Oil Seals

Several conditions must be met for the oil seals to function properly. These factors are:

• The oil seal mounting shaft should be ground with a surface finish or roughness between 0.2 and 0.8 microns. The shaft should be hardened to at least 40 to 45 HRc. to avoid groove formation on the shaft due to the spring's pressure.
• To avoid wear grooves, which typically tend to wear out the oil seal's lip more quickly, the area where the oil seal is positioned must be plunge ground.

Choosing the Correct Oil Seal Supplier

To ensure you have the most beneficial outcome when purchasing oil seals from an oil seal supplier, it is important to compare several companies using our directory of oil seal suppliers. Each oil seal supplier has a business profile page highlighting their areas of experience and capabilities, along with a contact form to directly communicate with the supplier for more information or request a quote. Review each oil seal business website using our patented website previewer to quickly learn what each company specializes in. Then, use our simple RFQ form to contact multiple oil seal companies with the same form.